System and Method of Battery Life Estimation

ABSTRACT

A device which includes a plurality of substantially identical batteries coupled via switching circuits to a power bus. Control circuits coupled to the batteries and the switching circuits to provide electrical energy to the bus from each of the batteries during a sequence of predetermined time intervals wherein one of the batteries provides electrical energy to the bus during a greater percentage of each tie intervals than the others of the plurality. Estimating remaining battery life of the others of the plurality in response to sensing that the one battery is substantial discharged.

FIELD

The application pertains to management of multiple batteries inelectrical devices. More particularly, the application pertains tosystems and methods for estimating remaining battery life.

BACKGROUND

One of the problems associated with battery powered devices is correctlyestimating the remaining battery life. It is useful to be able tocorrectly estimate this parameter because it facilitates programming thereplacement of the batteries. Such programs are particularly useful whenthe battery powered devices are part of a more complex system where morethan one device is to be monitored. For example, wireless fire detectionsystems can include hundreds of installed devices and it is important tocorrectly program the maintenance activities.

Various problems are present in determining the remaining battery lifeof a system. Common problems can include one or more of the following.Battery performance can strongly depend on the environmental condition,especially temperature (the battery life is strongly reduced at lowtemperatures). The performance of a battery strongly depends on the typeof usage. For example, high current sink for short periods, constantsink for long periods. Battery life depends on the aging of the battery.A battery can stay on the shelf an undetermined period before beinginstalled. Additional problems include, output voltage characteristics.The voltage output of some types of batteries, such as lithium iontypes, is constant for most of their life, having a rapid fall ofvoltage with a sharp knee at the end of their life.

These above noted characteristics make it difficult to estimate thebattery life by only measuring the output voltage or simply measuringthe time from the installation. It is obvious that being tooconservative in battery life estimation has a negative impact on thefrequency of maintenance services as well as a negative impact on theenvironment. It is preferable that batteries that are not completelyexhausted are not replaced too soon.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of an apparatus in accordance herewith.

DETAILED DESCRIPTION

While disclosed embodiments can take many different forms, specificembodiments hereof are shown in the drawings and will be describedherein in detail with the understanding that the present disclosure isto be considered as an exemplification of the principles hereof, as wellas the best mode of practicing same, and is not intended to limit theclaims hereof to the specific embodiment illustrated.

In one aspect hereof, battery life estimation can be incorporated intodevices that are powered by two or more independent identical batteriesin combination with control circuits. For example, a microcontroller incombination with interface circuits can be used to implement the presentmethod.

An example with four independent batteries is described subsequently.Those of skill will understand that the apparatus and methods hereof canbe used with any number of batteries, depending on the characteristicsof the devices being powered by the batteries.

In accordance herewith, different batteries can be used for differentpercentages of time. In another aspect, all the batteries are usedroutinely. This is desirable given the characteristics of batterycontacts. One of the batteries is used more extensively than the others.When this battery becomes discharged, the output voltage can bemeasured. Knowing the period for which it has been used, the remaininglife of the other batteries can be estimated.

It will be also be possible to calculate the percentage of use ofremaining batteries in order to make a determination as to when only onebattery will be charged. The remaining life for this battery can then bedetermined.

The method will give reliable results since the battery life is measuredin real conditions of use. Additionally, supposing the batteries havecome from the same batch, highly probable in commercial systems, “on theshelf” aging can be taken into account.

Advantageously, the present method differs from the current methodswhich estimate the remaining life by only measure the voltage on thebatteries. An assumption is then made as to the relationship between thevoltage and the remaining battery life.

By way of an example using four batteries, we can use battery number onefor 100% of the time and to not use the others at all. When this batteryreaches the end of its life (determined by measuring the outputvoltage), we can say that we have three times this duration of batterylife left in the remaining batteries.

Suppose that this time has been measured and is a duration of twelvemonths and we want the process to finish with two batteries completelyexhausted and one with six months of remaining life. In this instance,we have a total available life of 12×3=36 months. In 36−6=30 months wewant to use all the power of two batteries and just half the power ofthe other one. This means that we have an estimated battery life oftwenty four months for the 2 batteries (24/30=80% of the time) while thethird one is to be used for half of the estimated battery (6/30=20% ofthe time).

This calculation can be extended to a generic number n of batteries(n>=2), with a generic estimated life (Tlife) from the first part of themethod, and for a generic remaining life of the last battery(Tleft<=Tlife).

In accordance with the above:

% of usage of last battery=(Tlife−Tleft)/(Tlife(n−1)−Tleft)

% of usage of other batteries=(n−2)Tlife/(Tlife(n−1)−Tleft).

It is understood that the percentage of use must be distributed in timein order to have all the batteries working in all conditions. Forexample, not having one battery working during daytime and the otheronly at night because the environmental conditions and workload could bedifferent.

FIG. 1 illustrates an exemplary apparatus 10 which implements the abovedescribed process. Apparatus 10 can, for example implement a wirelessambient condition detector of smoke, gas, flame or the like all withoutlimitation.

Apparatus 10 can be carried by a housing 12. Housing 12 can carry aplurality of identical batteries 16 having members 16 a, b, c, and d. Itwill be understood that the use of four batteries is exemplary only andis not a limitation hereof.

Housing 12 can also carry control circuits 18. Control circuits 18 caninclude battery switch management circuits 18 a which, via switchingelements indicated at 20, can couple one or more of the batteries 16 toa power bus, indicated at 22, for the apparatus 10. The control circuits18 can include voltage measurement circuits 18 b which can be used tomeasure operating parameters, for example output voltage of each of thebatteries 16 a, b . . . n. The control circuits 18 can be implemented atleast in part by a programmed processor 18 c and local control circuitry18 d which is executed by processor 18 c.

Interface circuits 26, coupled to control circuits 18 can be used tocouple signals to/from one or more ambient condition sensors 28 a,output devices 28 b or communication interfaces 28 c. All of theelements 18, 26 and 28 can be powered off of the bus 22.

In operation, apparatus 10 can carry out analysis of batteryperformance, on a per apparatus, or device, basis, as described above.Results can be coupled via wireless interface 28 c to a displacedmonitoring system 30. It will be understood that the monitoring system30 can be in communication and control a plurality of devices, 10-1, -2,-3 . . . -n such as the device 10 without limitation.

In accordance herewith a battery management program can be implementedusing system 30 across a plurality of devices 10, 10-1, -2 . . . -n. Thedevices 10-1, -2 . . . -n can be installed in a region R which thesystem 30 is monitoring.

In summary, a device and a method are provided in which a plurality ofsubstantially identical batteries are coupled via switching circuits toa power bus. Control circuits coupled to the batteries and the switchingcircuits provide electrical energy to the bus from each of the batteriesduring a sequence of predetermined time intervals wherein one of thebatteries provides electrical energy to the bus during a greaterpercentage of each tie intervals than the others of the plurality.Remaining battery life of the others of the plurality is estimated inresponse to sensing that the one battery is substantial discharged.

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the spirit andscope of the invention. It is to be understood that no limitation withrespect to the specific apparatus illustrated herein is intended orshould be inferred. It is, of course, intended to cover by the appendedclaims all such modifications as fall within the scope of the claims.

Further, logic flows depicted in the figures do not require theparticular order shown, or sequential order, to achieve desirableresults. Other steps may be provided, or steps may be eliminated, fromthe described flows, and other components may be add to, or removed fromthe described embodiments.

1. An apparatus comprising: first circuitry to sense voltage output froma plurality of batteries, so as to use all of the batteries at leastintermittently, and to selectively switch among the members of theplurality wherein one of the batteries is used to provide energy tolocal elements wherein a selected battery is used for a greaterpercentage of a predetermined time interval; second circuitry todetermine when the selected battery has been discharged in accordancewith a predetermined discharge parameter; and third circuitry toestimate a remaining lifetime of the other members of the plurality. 2.An apparatus as in claim 1 further comprising a housing that carries thecircuitry along with at least one ambient condition sensor.
 3. Anapparatus as in claim 1 which includes a programmable processor andbattery switching circuits coupled to the circuitry.
 4. An apparatus asin claim 3 where the second circuitry establishes a life-time parameterfor the selected battery.
 5. An apparatus as in claim 4 which includesestablishing a remaining life-time parameter for the rest of thebatteries.
 6. An apparatus as in claim 2 which includes a programmableprocessor and battery switching circuits coupled to the circuitry andwhich determines when the selected battery is substantially discharged.7. An apparatus as in claim 6 which determines a usable remainingoperating interval for the remaining batteries.
 8. An apparatus as inclaim 7 with circuitry to transmit an indicator as to the remainingoperating interval to a displaced location.
 9. An apparatus as in claim2 where the sensor is selected from a class which includes at least asmoke sensor, a gas sensor, a fire sensor, a temperature sensor, ahumidity sensor, a motion sensor, a radiant energy sensor, and aposition sensor.
 10. An ambient condition detector comprising: at leastone sensor; a plurality of batteries; control circuits coupled to thebattery switching circuits to provide electrical energy intermittentlyfrom the members of the plurality of batteries and where the batteriesare switched such that all of the batteries are used to provide energyto the control circuits on an intermittent basis, during a sequence ofpredetermined time intervals.
 11. An apparatus as in claim 10 where oneof the batteries is used for a greater percentage of each of thepredetermined time intervals than are the remaining batteries.
 12. Anapparatus as in claim 11 wherein the one battery is intermittentlytested to determine an output characteristic, and in response thereto,generating an indicator to provide an indicium of remaining life of allother members of the plurality.
 13. An apparatus as in claim 10 whichincludes at least one of a smoke sensor, a gas sensor, a fire sensor, atemperature sensor, a humidity sensor, a motion sensor, a radiant energysensor, and a position sensor.
 14. An apparatus as in claim 12 whichincludes at least one of a smoke sensor, a gas sensor, a fire sensor, atemperature sensor, a humidity sensor, a motion sensor, a radiant energysensor, and a position sensor.
 15. A method of estimating remaining lifeof a group of batteries comprising: providing a group of batteries;using all of the batteries intermittently during each of a sequence ofpredetermined time intervals to provide electrical energy to a loadwherein a selected battery is used for a greater percentage of time thaneach of the other members of the group during each predetermined timeinterval; determining when the selected battery is substantiallydischarged; determining a remaining life parameter for the remainingbatteries; and using the determined remaining life parameter in carryingout a battery replacement process.
 16. An apparatus as in claim 15 whichincludes determining a percentage of use of the remaining batteries toestablish when all but one of those batteries will be discharged.
 17. Anapparatus as in claim 16 which includes establishing a remaining lifeparameter of the one battery.
 18. An apparatus as in claim 16 whichincludes transmitting an indicium as to a remaining life parameter ofthe one battery to a displaced location.